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PROFESSIONAL PAPERS No. 4 

CONTRIBUTIONS'TO ENGINEERING CHEMISTRY 
BY MEMBERS OF THE STAFF OF 
ARTHUR D. LITTLE, Inc., CHEMISTS £9' ENGINEERS 

THE BASIS OF QUALITY 
IN PAPER 

BY 

ARTHUR D. MTTLE 

OFFICIAL CHEMIST. AMERICAN PAPER AND PULP ASSOCIATION 




93 BROAD STREET 
BOSTON 

1910 



itonograpii 



THE WORK OF THIS LABORA- 
TORY of Engineering Chemistry is 
primarily directed toward increasing 
the efficiency of Industrial Effort by aiding 
manufacturers, public service corporations and 
individual clients in the economic selection of 
raw materials, the chemical control of pro- 
cesses and product and the study of special 
problems. 

The Laboratory organization, which is the 
most complete in the country in its field, 
includes specialists in mechanical, fuel, turbine, 
gas and electrical engineering, and in all 
departments of applied chemistry, who have 
been selected equally with reference to their 
initial scientific training and wide practical 
experience. 

Correspondence regarding the service of 
this Laboratory as applieid to any particular 
problem, plant or industry is invited and will 
receive prompt attention. 



ARTHUR D. LITTLE, Inc.. 



93 Broad St., 

Boston, Mass. 



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The Basis of Quality 
in Paper 

By ARTHUR D. LITTLE 

TXyTHEREAS a few not greatly varying sorts of paper were 
^ ' enough to satisfy the very moderate requirements of 
our grandfathers, the development of modern conditions has 
brought such complexity into social and commercial life, 
and extended so enormously the range of industry as to 
increase by many thousandfold the demands of the com- 
munity upon the paper maker. In his efforts to meet these 
demands the paper maker has been greatly aided by count- 
less discoveries and inventions, without which indeed the 
demands could not have been met at all. New sources of 
raw material, new methods of treatment, new machines, and 
altogether new agencies of many kinds have been added 
to the resources of the art. As a result the consumer now 
finds available for his widely-diverse purposes thousands of 
kinds of paper which exhibit in their composition and 
properties the extremes of possible variation in a multitude 
of factors. 

Amid such bewildering variety how is quality to be 
determined ^ What constitutes the basis of quality in 
paper ^ 

The Germans long ago, after extended investigation, 
established and have since developed and maintained under 
government regulations, a system of classification of papers 
based on their composition and physical properties. This 
classification or definition of so-called "Normal Papers" 
has since attained a considerable acceptance in countries 
other than Germany and has come to be regarded as con- 
stituting a series of standards of quality in paper. Valuable 



IJ-RQ-qi 



as this system of classification has proved itself to be to both 
users and makers of paper, and indispensable as the refined 
and accurate testing methods which it involves have become 
for the intelligent selection of papers, it remains true, never- 
theless, that, taken by itself, or as applied to any particular 
papers without reference to their intended use, it is without 
significance as to quality. There is, in a word, no such thing 
as a general basis for quality in paper, and no other possible 
basis for quality in case of any particular paper than its 
suitability for its intended use. Good writing paper is bad 
blotting; good news print is poor wrapping; good book 
paper is an impossible cigarette paper; and so on. In no 
case can the properties of good paper be defined until the 
specific use for which the paper is intended has been stated 
or assumed. The properties which confer high quahty 
upon a paper intended for one purpose are precisely those 
which condemn it for another. Stretch is a desirable property 
for a bag paper, it may be fatally objectionable in paper 
for lithography; opacity is a principal element in deter- 
mining the quality of bible paper, transparency is equally 
important in pergamyn and glassine papers. Certain grades 
of book papers base their claims to quahty mainly upon 
the extent to which they bulk for weight; the buyer of 
wrapping paper should consider, on the other hand, area 
for weight in determining quality. 

Keeping clearly in mind, then, the conclusion that the 
basis of quality in paper must always be found in the rela- 
tion of the properties of particular papers to the intended 
purpose of these papers, let us consider the more important 
properties of the material and their relation to particular 
uses. 

In case of a thing so apparently simple in its make-up 
as a sheet of paper, an extraordinary number of factors are 
involved in any consideration of its quality. Many of these 
factors are elusive, in the sense of evading exact definition 
or determination, but they are none the less important, or 
even at times decisive, on that account. Such, for example, 
are permanency, feel, texture, finish, rattle, tear, formation, 



'SUB 



fastness of color, distinctness and artistic quality of water- 
marking, dirt, softness, hardness, hairiness, or "whiskers," 
distinctive appearance, "color" of white papers, printing 
quality and ability to withstand erasure. As to most of 
these properties reliance must be placed upon expert judg- 
ment and comparison with standard or accepted samples 
of generally similar papers. Permanency, however, is largely 
a function of composition, and the composition of a paper 
can be determined with a considerable degree of accuracy. 
No paper, therefore, which is intended for permanent 
records should contain ground wood, unbleached fiber of 
any kind, acid, sulphur, soluble chlorides, or more than a 
moderate amount of ash. Preferably, it should be free from 
resin, and in the absence of conclusive proof of the perma- 
nent character of papers made from well prepared chemical 
wood fibers, preference should be given to all rag papers. 
Since over-bleaching hastens the deterioration of fibers, 
extreme whiteness is undesirable in the sheet. 

In case of papers for ephemeral uses, permanency has, 
of course, little bearing upon quality. For printing upon 
fast perfecting presses, newspaper is better paper because 
of the large proportion of ground wood it contains, and to 
which it owes in great measure its special printing quality. 

Fastness of color, while not permitting of exact quantita- 
tive determination, can, nevertheless, be tested experi- 
mentally with sufficient accuracy for most purposes, while 
very definite conclusions may often be drawn from the 
known degree of fastness of the dyes or pigments from 
which the paper derives its color. Fastness of color is of 
comparatively little importance as affecting the quality of 
papers intended to serve a temporary purpose. It becomes 
of prime importance in wall papers, etching, photograph 
mounts, plate papers, map and fine book paper. Similarly 
uniformity of color has slight influence on the quality of 
small lots of paper, especially if these are to be used as 
single sheets. It does bear directly upon the quality of paper 
for serial publications which are to be bound together. 
With the invention of the Ives Colorimeter the color of 



paper has fortunately become a property permitting of exact 
measurement and definition. 

For almost all purposes the presence of a noticeable 
amount of dirt is regarded as detrimental to the quality of 
paper. It not only detracts from the appearance of the 
paper, but its presence may be indicative of the use of 
inferior or carelessly prepared material. In some few cases, 
as with wrappers made from screenings, the dirt may be 
so considerable in amount, and so uniformly distributed as 
to become an integral and characteristic part of the paper, 
while as with certain Japanese papers dirt in the form of 
unreduced bark or vegetable tissue may be so disposed 
within the sheet as to actually enhance its quality from the 
artistic standpoint. While it is not easy to give numerical 
expression to the amount of dirt present in a sheet, the 
experienced paper maker or paper buyer has no difficulty 
in making close comparisons in this regard. It is by no 
means so easy to estimate exactly the bearing of relative 
amounts of dirt upon quahty. 

Fortunately, what may be called the fundamental proper- 
ties of paper permit in nearly every case of exact measure- 
ment and numerical statement. These fundamental proper- 
ties are thickness, weight per unit area, resistance to bursting 
strain, tensile strength in different directions, stretch, ability 
to resist wear, tendency to absorb ink or water, opacity. 
Furthermore, these properties are largely determined by the 
composition of the paper, and the care and skill with which 
its material has been prepared and manipulated during 
manufacture. Fortunately, again the composition can be 
accurately determined by chemical and microscopical exami- 
nation while at the same time many direct and important 
inferences may be drawn from these examinations as to the 
course and nature of the processes of manufacture. 

Of all the fundamental properties, thickness is perhaps 
most easily determined . Differences of a few ten-thousandths 
of an inch are instantly detected by trained fingers, and the 
exact measurement of thickness to ten-thousandths of an 
inch is easily made by means of several forms of micrometer 



employed In paper testing. Thickness bears directly upon 
quality in case of most papers, but the way in which it bears 
is determined always by the purpose for which the paper is 
intended. Bible papers, onion skin, kraft, pergamyn, con- 
denser paper, tissues generally, and many other special 
sorts gain in quality, as represented by money value, with 
decrease of thickness, partly because of increased difficulty 
and cost of manufacture, but principally because they better 
meet the necessities of the consumer. Other things being 
equal, a manifold paper which permits the making of ten 
copies is obviously a better paper for its purpose than one 
which cannot be used for more than five. The quality and 
value of the paper used for building up electrical condensers 
is enormously influenced by the relative thinness of the 
paper, since the efficiency of the condenser depends largely 
upon the closeness with which the tin foil plates are brought 
together; but while thinness is thus important, quality in 
this case is finally determined by absence of pin holes, the 
presence of which entirely destroys the value of the paper 
for its purpose. 

Weight per unit area is a quality factor of varying im- 
portance, although since paper is sold by the pound the 
lighter of two otherwise equally satisfactory papers is 
commonly to be preferred. This does not always hold, 
however, as in case of paper for conversion into celluloid. 
With wrapping papers weight per unit area becomes of the 
first importance, and when low and combined with strength 
commands the market, as evidenced by the rapidly extend- 
ing popularity of kraft paper. With cover papers a small 
increase in weight may double the cost of mailing pamphlets, 
while obviously at equal prices per pound the cost of paper 
for printing a given number of pages is proportional to the 
weight per unit area. 

Weight for bulk influences quality for most purposes, 
and is especially important in connection with book papers, 
blottings, matrix papers and box boards. With book papers, 
indeed, this factor is often a good exponent of general quality, 
since low weight for bulk implies a minimum of filler, the 



use of high-grade stock and skilful treatment in the beater. 
English book papers are notable for their bulking property 
and moderate weight. Where an edition involving a number 
of volumes of varying amount of text is to be made, the 
bulking property of the paper for the different volumes 
should be in inverse proportion to the number of pages in 
the volumes in order that the volumes themselves shall run 
uniform in size. Laid papers bulk more than wove papers 
of the same composition, and the bulking quality of different 
fibers varies over a wide range, esparto making an especially 
bulky paper. The use of mineral fillers, prolonged beating, 
hard calendering, coating and especially the addition of 
barytes to the coating mixture, all tend to make the paper 
thin for weight. They are justified only to the extent to 
which they may compensate by affecting other quality 
factors favorably. 

Strength, whether measured as resistance to bursting 
strain, resistance to direct pull, or determined roughly by 
mere tearing, is commonly regarded as one of the most 
direct evidences of quality. There is a large measure of 
justification for this conclusion since high strength generally 
implies good stock, carefully prepared and skilfully manipu- 
lated. A certain minimum of strength, which, however, 
varies greatly with the class of paper, is an essential pre- 
requisite of quality; while with special sorts of paper, as bag 
paper, kraft, paper for tags, twine, cartridge cases, etc., 
strength almost determines quality provided it is not asso- 
ciated with brittleness which makes the paper weak to 
sudden strain. With envelope papers, strength after folding 
is far more important than the strength of the flat paper. 
Curiously, rosin sizing reduces strength, and "wild" papers 
are commonly stronger than similar papers showing good 
formation. The " strength ratio " affords the most convenient 
way of reporting strength of papers. It is the quotient 
obtained by dividing the strength in pounds as determined 
by the Mullen tester, by the thickness in ten-thousandths 
of an inch. A paper 35-10,000 thick which tested thirty-five 
pounds would, therefore, have a strength ratio of i.e. The 

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strongest commercial papers seldom or never show a strength 
ratio higher than 2.0, although we have recently prepared 
samples by special methods with the extraordinarily high 
ratio of 3.8. 

The stretch of paper commonly ranges from i to 4 per 
cent. The amount of stretch shown by the paper affects 
quality favorably or otherwise according to the require- 
ments of use. A large proportionate stretch improves the 
quaHty of bag papers, cartridge paper, drawing, matrix and 
paper for twine, artificial leather and embossing. It is very 
objectionable in lithograph, coated and many printing 
papers requiring close register, as also in paper for music 
rolls for mechanical organ and piano players. 

In this country, up to the present time little or no atten- 
tion has been paid to what in case of most papers is one of 
the most reliable and significant indications of general 
quaHty, namely the ability of the paper to withstand wear. 
Paper for money or for permanent records, loose leaf books, 
maps, school books, works of reference, blue prints, chil- 
dren's books, wrapping, card stock for catalog files, folders, 
and many other uses, should exhibit this property in the 
highest degree consistent with other requirements of the 
specification. Although in the past rehable methods and 
apparatus have not been available, in the United States 
at least, for determining wearing power, there is no longer 
any excuse for ignoring this essential element of quality, 
the numerical value of which may now be determined with 
the utmost accuracy with standard apparatus. 

The capillary power of a paper, or its tendency to absorb 
ink or water, may be given suflSciently accurate expression 
by simple methods of testing. The bearing of the results 
upon quality depends entirely upon the class of paper 
tested. With due regard to other factors, the quality of 
writing papers rises as the capillary power falls, the quality 
of blotting paper is almost wholly determined by its capil- 
lary power; matrix papers and papers for celluloid manu- 
facture or for conversion into parchment paper, vulcanized 
fiber or roofing must have high capillary power, that of 



printing papers should generally be only moderate if the 
best results in rapid printing are to be secured. 

The determination of opacity is more difficult, although 
this property is often one upon which the quahty of paper 
in large part depends as in case of bible paper, envelope 
paper, and book papers generally. A considerable degree 
of translucency upon the other hand is a mark of quality 
in bond papers, while for other writings opacity commonly 
suggests quality. In parchment paper, again, quahty pre- 
supposes translucency, while pergamyn papers of good 
quality must be almost transparent. 

These physical properties of paper which, taken together, 
and interpreted with reference to the use for which the 
paper is intended, are almost conclusive as defining quality, 
are nevertheless themselves largely functions of the compo- 
sition of the sheet. For this reason any final estimate of 
quality must include consideration of the sorts of fiber 
present, their condition and proportion, the kind and 
amount of filler, the proportion and sorts of size, and the 
presence or absence of acid, bleach residues, and other 
chemicals likely to cause deterioration or otherwise impair 
quality. 

Although paper of some sort may be made of almost any 
vegetable fiber, the number of fibrous raw materials economi- 
cally available for paper making is, in view of the almost 
infinite variety of vegetation, surprisingly limited. Cotton, 
flax, jute, straw, esparto, hemp and a few woods almost 
exhaust the list. Nevertheless, not only does each of these 
fibres impart definite and often distinctive characteristics 
to the sheet into the composition of which it enters, but the 
range of variation is further enormously increased by ad- 
mixture of several fibres, and the chemical and mechanical 
treatment which they have received by way of preparation. 
The best stock for any paper is easily spoiled by careless or 
improper methods. The stock that under skilful treatment 
normally yields a strong, tough, permanent sheet, may by 
improper beating or careless bleaching give only a weak, 
brittle and short-lived paper. The degree to which the 

8 



fiber substance is hydrated during beating has a profound 
effect upon the properties of the paper, as also the manner 
in which the fibers themselves have been subdivided. All 
this, of course, to the papermaker himself is the mere 
A B C of his art, but it is commonly unknown to the paper 
consumer or ignored by him in his estimates of quality. 
Quality cannot be predicated upon stock alone. It is, 
nevertheless, true that for many papers, especially those 
intended for writing and the higher grades of printing, the 
properties representative of the highest quality are not 
obtainable except through the use of a large proportion of 
rag stock. For insulating papers such as cable paper, 
however, manila stock is distinctly better than rag, and 
curiously enough, so is even a Hme cooked straw pulp. 
Where great toughness is desirable, as in tag and certain 
wrapping papers, the highest quahty is obtainable only 
through use of manila and similar bast fibers. 

The relation of the wood fibers to quality has been a 
matter of controversy since the time of their introduction. 
As to ground wood, there is probably now no question of 
its unsuitability for practically every use involving per- 
manency, since exposure for even a few hours to direct 
sunlight renders ground-wood papers weak and brittle. It 
is particularly undesirable in so-called manila papers in- 
tended for making envelopes, which, if containing much 
ground wood quickly lose all strength on the fold under 
the influence of sunlight. For wall papers, rather strangely, 
ground wood does not seem open to much objection, partly 
because no great strength is required of such papers, but 
principally because the surface coating with size and color 
protects the paper beneath. For newsprint paper, ground 
wood remains the only possible material in spite of some 
minor disadvantages for such use. 

Sulphite and soda fiber, if thoroughly well cooked and 
carefully bleached, are probably nearly, and perhaps quite 
as permanent as rag stock. In fact, the examination of 
over 400 samples of paper from the library of the University 
of Berlin showed that papers composed wholly or in large 



part of chemical wood fiber gave slightly less evidence of 
deterioration than all rag papers. Since the better grades 
of rag stock are considerably more expensive than chemical 
wood fibre, endow the paper with more wearing power and 
better feel and texture, the presence of wood fibers is, in 
most cases, properly regarded as tending to lower quality. 
They are highly objectionable n papers for making parch- 
ment and vulcanized fiber, which should consist wholly of 
cotton rag stock. 

The number of cases in which mineral filler improves the 
quality of paper is comparatively limited, although it is 
well recognized that for certain-uses a moderate amount of 
filler reacts favorably upon quality, by increasing opacity, 
and improving feel and finish. Filler invariably, however, 
lowers strength and resistance to wear, diminishes bulk for 
weight and tends toward brittleness. In many special 
papers it is wholly inadmissible. 

The number of factors which are concerned with the 
quality of paper in its multitudinous applications to special 
uses is so great as to prevent consideration or even enumera- 
tion of them all. A paper for wtapping hardware or a card 
for mounting silver jewelry may seem to possess every 
desirable property, and yet be worse than useless because 
of a trace of sulphur. A printing paper may develop 
"whiskers" or clog the type by mineral filler, a coated 
paper may pick or develop odor, a cigarette paper may 
burn badly, a writing paper may allow the ink to spread 
because the size has been converted into peptones by over- 
heating, a filter paper may fail to hold a fine precipitate 
or unduly retard the passage of liquid, and so on. Enough 
has been said to suggest to consumers of paper the com- 
plexity of the problems involved in the determination of 
quality, the importance of paper testing, and the advantages 
to both maker and consumer of carefully considered and 
intelligently drawn specifications defining quality as a 
function of intended use. 



10 



ARTHUR D. LITTLE, Inc. 

CHEMISTS AND ENGINEERS 



FUEL ENGINEERING DEPARTMENT 

D. T. RANDALL, Engineer in charge. 
Coal Analysis — Fuel Economies — Smoke Abatement — 
Design, Construction and Expert Operation of Power 
Plants, Acceptance Tests. 

GAS ENGINEERING DEPARTMENT 

PERRY BARKER, Chemical Engineer in charge. 
Gas Analysis — Expert Operation of Producer and Illumin- 
ating Gas Plants — Reports on Properties. 

ELECTRICAL ENGINEERING DEPARTMENT 

J. G. CALLAN, Electrical Engineer in charge. 
Acceptance Tests on Electrical Equipment and Steam 
Turbines — Advice, Reports, Designs. Specifications for 
Material and Equipment. 

ELECTRIC RAILWAY DEPARTMENT 

C. F. WOODS, Chemical Engineer in charge. 
Inspection, Chemical Analyses and Physical Tests of all 
material and supplies — Specifications — Timber Preserva- 
tion — Electrolysis Surveys. 

PAPER AND PULP DEPARTMENT 

A. D. LITTLE, Chemist in charge. 
Analysis of Supplies — Control of Processes — Efficiency 
Studies — Reports on New Materials, Methods and Special 
Products — Pulp Sampling — Paper Testing — Specifica- 
tions — Design of Special Plants, 

TEXTILE DEPARTMENT 

W. S. WILLIAMS, Chemical Engineer in charge. 
Expert Advice in Boiling — Bleaching — Mercerizing — 
Dyeing — Finishing and all processes of fiber treatment — 
Evaluation of supplies — Yam and Cloth Testing — Cloth 
Analysis. 

RESEARCH* DEPARTMENT 

F. E. GALLAGHER, Chemist in charge. 
Industrial Research — Report's on new processes and 
products — Study of Special Problems. 

GENERAL LABORATORY DEPARTMENT 
H. J. SKINNER, Chemist in charge. 
Chemical Analyses of all materials — Iron — Steel — Alloys — 
Lubricants — Paints — Cement — ^\Vater — Foods — Mill Sup- 
plies — Factory Wastes. 

Contract Service, as desired, In all Departments. 



018 371 467 3 



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LIBRARY OF CONGRESS 

018 371 467 3 • 



